Can't leave you unanswered so here's my far-from-expert view...
This is very much a 'how long is a piece of string?' question. The answer depends on -
Do you think the house is fairly priced at this level? What are other houses in the area selling for?
Where is the house? Are properties selling like hot cakes where you are or languishing on the market? There are definitely some areas of the country where demand is high and supply is low for certain types of property.
How long has the house been on the market? If it's been sitting about, the vendors may well take an offer.
What's your position? A first time buyer with finance in place may well get away with a cheekier offer than someone who is yet to sell their own property - if the vendors are keen to get going at least.
I don't have experience of guide ranges but what it boils down to is this - how much do you want the house and how much are you willing to pay? Would you be gutted if you lost the property for the sake of £5K for example? If you are intending to live there for a long time then a few extra thousand isn't such a big deal.
I don't know if that helps but there are so many factors involved that it's hard for anyone to tell you what to do.
We recently moved into a house which, barring unforeseen events (!), we are intending to spend the next 10-15 years in. We ended up paying slightly over asking price but it didn't matter - we can still afford it, we are intending to be there for ages, it will suit our family perfectly as they grow up (schools etc), very few suitable properties have been coming onto our local market and those which are half-decent are being snapped up. Our own property sold for asking price (which was a bit over a stamp duty level) in 4 days - because the demand was there.
As it stands, we have seen perhaps one or two contenders come up since we bought our home almost 3 months ago...it's that desperate! So, we're happy with what we paid. Others might not have considered it worth it, depending on their own circumstances.
This is very long now. Hope it gives you a few things to consider though...